Variable dual spring blade root support for gas turbines

Abstract

An adjustable blade root spring device for turbine blade fixation in turbomachinery. The device is designed to be placed in a space in a rotor disk cavity adjacent to a tip of a blade root, where the device applies a radial outward force on the turbine blade to fix the blade position in the rotor disk. The device includes a wave spring with integral end blocks which is compressed by a bolt and a coil spring. When the wave spring is compressed in length, it increases in height and makes contact with the rotor disk and the turbine blade. The force of the wave spring on the turbine blade can be adjusted via the bolt, and the coil spring provides an increased compliance range. The body of the device has an oblong cross-sectional shape, thereby preventing rotation of the device in the space between the blade and the disk.

What is claimed is: 
     
       1. An adjustable blade root spring device for fixing a turbine blade in position in a rotor disk in a gas turbine, said device comprising: an outer body including opposing side walls and first and second ends, where the outer body has a cross-sectional shape approximating an ellipse with flat sides parallel to its major axis, and the outer body has a central opening bounded by the side walls and open on top and bottom; a wave spring comprising a plurality of straight segments folded in an alternating fashion into a wave shape, with an apex point between each of the plurality of straight segments, where the wave spring includes a floating end block at a first end and a fixed end block at a second end, and where the wave spring is placed substantially within the central opening of the outer body such that the floating end block is outside of the first end of the outer body and the fixed end block is fitted into a slot in the second end of the outer body; a coil spring; a flat washer; a bent tab washer; and a bolt, said bolt arranged to pass through the bent tab washer, the flat washer, and through the coil spring and then through a hole in the floating end of the wave spring, said bolt being threaded into a threaded hole in the first end of the outer body, where threading the bolt into the threaded hole compresses the coil spring against the floating end and causes the wave spring to decrease in length and increase in height such that the wave spring presses the turbine blade radially outward relative to the rotor disk. 
     
     
       2. The device of  claim 1  wherein the turbine blade includes a root portion having an inverted fir tree shape, the rotor disk includes a cavity shaped to receive the root portion of the turbine blade, and the cavity further includes a space adjacent to the root portion of the turbine blade where the device can exert a force radially outward on the turbine blade and radially inward on the rotor disk. 
     
     
       3. The device of  claim 2  wherein the flat washer has a shape which matches the cross-sectional shape of the outer body, and where the shape fits within the space adjacent to the root portion of the turbine blade but does not permit rotation of the flat washer or the outer body within the space. 
     
     
       4. The device of  claim 2  wherein the wave spring presses the turbine blade radially outward relative to the rotor disk with a force of at least 150 pounds, and the force fixes the turbine blade in position in the rotor disk in any static or dynamic configuration of the gas turbine. 
     
     
       5. The device of  claim 4  wherein the coil spring has a stiffness which causes the coil spring to compress by a compression amount when the bolt is tightened during installation of the device, and the compression amount is sufficient to absorb any relaxation of the wave spring due to increased height of the space adjacent to the root portion of the turbine blade during turbine operation, while still maintaining the force of at least 150 pounds. 
     
     
       6. The device of  claim 5  wherein the stiffness of the coil spring is in a range of 150-200 pounds/inch. 
     
     
       7. The device of  claim 1  wherein the bent tab washer includes an engagement tab which engages a notch in the flat washer and prevents rotation of the bent tab washer relative to the flat washer, where tabs on the bent tab washer can be bent into a position which prevents rotation of the head of the bolt after the device has been installed in the gas turbine. 
     
     
       8. The device of  claim 1  wherein the wave spring, including the floating end block, the fixed end block and a spring section therebetween, is machined from a single piece of a nickel-based alloy. 
     
     
       9. The device of  claim 8  wherein the spring section has a width in a range of 0.15-0.30 inches and a nominal thickness of 0.025 inches. 
     
     
       10. The device of  claim 1  wherein the wave spring is shaped so that four upper apex points contact the turbine blade and five lower apex points contact the rotor disk, and the four upper apex points are coplanar with upper surfaces of the floating end block and the fixed end block. 
     
     
       11. The device of  claim 10  wherein the four upper apex points each provide a substantially equal contact force on the turbine blade, and the five lower apex points each provide a substantially equal contact force on the rotor disk. 
     
     
       12. A gas turbine engine rotor assembly, said assembly comprising: a plurality of turbine blades, each of the plurality of turbine blades including a blade root portion having an inverted fir tree shape; a rotor disk designed to hold the plurality of turbine blades in a circumferential arrangement around an outer periphery of the rotor disk, said rotor disk including a plurality of cavities, with one of the plurality of cavities for each of the plurality of turbine blades, where each of the plurality of cavities has a fir tree shape designed to receive the blade root portion of one of the plurality of turbine blades, and where each of the plurality of cavities also includes a space adjacent to and radially inward from the blade root portion; and an adjustable blade root spring device inserted into the space in each of the plurality of cavities, where the adjustable blade root spring device includes: an outer body including opposing side walls and first and second ends, where the outer body has a cross-sectional shape approximating an ellipse with flat sides parallel to its major axis, and the outer body has a central opening bounded by the side walls and open on top and bottom; a wave spring comprising a plurality of straight segments folded in an alternating fashion into a wave shape, with an apex point between each of the plurality of straight segments, where the wave spring includes a floating end block at a first end and a fixed end block at a second end, and where the wave spring is placed substantially within the central opening of the outer body such that the floating end block is outside of the first end of the outer body and the fixed end block is fitted into a slot in the second end of the outer body; a coil spring; a flat washer; a bent tab washer; and a bolt, said bolt arranged to pass through the bent tab washer, the flat washer, and through the coil spring and then through a hole in the floating end of the wave spring, said bolt being threaded into a threaded hole in the first end of the outer body, where threading the bolt into the threaded hole compresses the coil spring against the floating end and causes the wave spring to decrease in length and increase in height such that the wave spring presses the turbine blade radially outward relative to the rotor disk. 
     
     
       13. The rotor assembly of  claim 12  wherein the flat washer has a shape which matches the cross-sectional shape of the outer body, and where the shape fits within the space adjacent to the root portion of the turbine blade but does not permit rotation of the flat washer or the outer body within the space. 
     
     
       14. The rotor assembly of  claim 12  wherein the bent tab washer includes an engagement tab which engages a notch in the flat washer and prevents rotation of the bent tab washer relative to the flat washer, where tabs on the bent tab washer can be bent into a position which prevents rotation of the head of the bolt after the device has been installed in the gas turbine. 
     
     
       15. The rotor assembly of  claim 12  wherein the wave spring, including the floating end block, the fixed end block and a spring section therebetween, is machined from a single piece of a nickel-based alloy. 
     
     
       16. The rotor assembly of  claim 15  wherein both edges of the spring section of the wave spring are machined with a taper angle of between 9 and 11 degrees in order to provide improved clamp holding of the wave spring during subsequent machining operations. 
     
     
       17. The rotor assembly of  claim 12  wherein the wave spring is shaped so that four upper apex points contact the turbine blade and five lower apex points contact the rotor disk, and the four upper apex points are coplanar with upper surfaces of the floating end block and the fixed end block. 
     
     
       18. A gas turbine vibration reduction system; comprising:
 an outer body configured to reside in a space between a rotor disk and a blade root of a gas turbine rotor, said outer body having a cross-sectional shape which prevents rotation of the body within the space; a wave spring comprising a plurality of straight segments folding in an alternating fashion into a wave shape, with an apex point between each of the plurality of straight segments, said wave spring substantially contained within the outer body such that said wave spring includes a first end block fixed within the outer body and a second end block positioned outside the outer body; a compression screw arranged on an exposed end of the outer body such that the screw operatively adjusts a compression of the wave spring; and a coil spring arranged coaxially surrounding the compression screw and passing through the second end block of the wave spring to maintain a residual contact pressure between the compression screw and the wave spring. 
 
     
     
       19. The vibration reduction system of  claim 18  wherein the wave spring, including the first and second end blocks and a spring section therebetween, is machined from a single piece of a nickel-based alloy. 
     
     
       20. The vibration reduction system of  claim 18  wherein the wave spring is shaped so that four upper apex points contact the blade root and five lower apex points contact the rotor disk, and the four upper apex points are coplanar with upper surfaces of the first and second end blocks.